Various kinds of methods have been developed by which samples such as proteins and nucleic acids are separated and detected, taking advantage of their individual properties. Also, apparatuses used for the methods have been developed. Examples of the separation methods include gel electrophoresis, capillary electrophoresis, and liquid chromatography. Among these methods, gel electrophoresis has been widely used from the viewpoint of its easiness and realization of high resolution separation.
Gel electrophoresis is carried out in the following modes: electrophoresis by which a sample is separated in only one direction; and two-dimensional electrophoresis by which a sample is separated in two directions. The two-dimensional electrophoresis is generally carried out for analysis of proteins.
In a case where a protein is separated by two-dimensional electrophoresis, isoelectric focusing electrophoresis that uses a gel strip having a given pH gradient is used for separation in the first-dimensional direction. The isoelectric focusing electrophoresis is a method of applying a voltage across the gel strip to perform separation, taking advantage of differences in isoelectric points specific to proteins. Further, for the separation in the second-dimensional direction, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) using sodium dodecyl sulfate (SDS), which is an anionic surfactant, is widely used. The two-dimensional electrophoresis is widely used for proteome analysis because it enables separation of many proteins at once and comprehensive analysis of the proteins. Proteome is the term that indicates an entire protein into which translation is carried out in a particular cell, organ, etc. Examples of studies for the proteome include profiling, functional analysis, etc. of proteins.
Further, it is known that a protein synthesized in vivo is adjusted for its function by being subjected to chemical modification called post-translational modification, such as phosphorylation. The above-described electrophoresis can only separate a protein into different components. Therefore, only separation analysis is difficult to obtain information regarding post-translational modification of the components.
In proteome analysis, as a method for detecting a sample protein separated by electrophoresis, there is a method known as transfer (blotting) by which a sample separated in a gel is adsorbed and fixed to a transfer film. For the transfer film, a nitrocellulose film, a PVDF (Polyvinylidene difluoride) film, or the like film which is easy to be bound to a sample and is highly hydrophobic is used.
The sample having been transferred onto the film is detected with use of a fluorescent-labeled antibody, probe, or the like. As a method of detecting a protein with use of an antibody, Western blotting is known. By overlaying a particular antibody on a film having a protein transferred thereon, it becomes possible to specify a protein to some extent on the basis of antigen-antibody reaction. As to phosphorylation, which is biologically important post-translational modification, it is possible to detect the presence or absence of a phosphorylated protein, the differences between phosphorylation sites, and the like by overlaying an anti-phosphorylated antibody on the film subjected to protein transfer.
Thus, a combined use of electrophoresis and Western blotting is an extremely effective method for proteome analysis (for example, see Non-Patent Literature 1).
Conventionally, electrophoresis and Western blotting are carried out manually by researchers, using separate apparatuses. More specifically, it is general that after SDS-PAGE is carried out in an electrophoresis apparatus, a gel is taken out of the apparatus and moved in a transfer (blotting) apparatus, and then transfer (blotting) is carried out with a transfer film set on the transfer (blotting) apparatus. These operations are complicated and require some experience because the gel is a very soft material and therefore difficult to handle. However, there exists a technique (Patent Literature 1) that automates these operations. Patent Literature 1 discloses a technique of automating a series of operations from electrophoresis to Western blotting.